Integrated circuit wireless communication unit and method for providing a power supply

ABSTRACT

An integrated circuit is described for providing a power supply to a radio frequency (RF) power amplifier (PA). The integrated circuit comprises a low-frequency power supply path comprising a switching regulator and a high-frequency power supply path arranged to regulate an output voltage of a combined power supply at an output port of the integrated circuit for coupling to a load. The combined power supply is provided by the low-frequency power supply path and high-frequency power supply path. The high-frequency power supply path comprises: an amplifier comprising a voltage feedback and arranged to drive a power supply signal on the high-frequency power supply path; and a high-frequency-path supply module arranged to provide a high frequency supply to drive the amplifier, where the high-frequency-path supply module comprises a pulse-width modulator operably coupled to the high frequency supply via a filter and arranged to provide a filtered pulse-width modulated signal to the high frequency supply.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.13/345,760 (filed on Jan. 9, 2012), which claims the benefit of U.S.provisional application No. 61/438,347 (filed on Feb. 1, 2011) and U.S.provisional application No. 61/563,316 (filed on Nov. 23, 2011), andthis CIP application further claims the benefit of U.S. provisionalapplication No. 61/843,218 (filed on Jul. 5, 2013). The entire contentsof these related applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of this invention relates to wireless communication units,transmitter architectures and circuits for providing a power supply. Theinvention is applicable to, but not limited to, power supply integratedcircuits for linear transmitter and wireless communication units and apower amplifier supply voltage method therefor.

2. Description of the Prior Art

A primary focus and application of the present invention is the field ofradio frequency (RF) power amplifiers capable of use in wirelesstelecommunication applications. Continuing pressure on the limitedspectrum available for radio communication systems is forcing thedevelopment of spectrally-efficient linear modulation schemes. Since theenvelopes of a number of these linear modulation schemes fluctuate,these result in the average power delivered to the antenna beingsignificantly lower than the maximum power, leading to poor efficiencyof the power amplifier. Specifically, in this field, there has been asignificant amount of research effort in developing high efficiencytopologies capable of providing high performances in the ‘back-off’(linear) region of the power amplifier.

Linear modulation schemes require linear amplification of the modulatedsignal in order to minimise undesired out-of-band emissions fromspectral re-growth. However, the active devices used within a typical RFamplifying device are inherently non-linear by nature. Only when a smallportion of the consumed DC power is transformed into RF power, can thetransfer function of the amplifying device be approximated by a straightline, i.e. as in an ideal linear amplifier case. This mode of operationprovides a low efficiency of DC to RF power conversion, which isunacceptable for portable (subscriber) wireless communication units.Furthermore, the low efficiency is also recognised as being problematicfor the base stations.

Furthermore, the emphasis in portable (subscriber) equipment is toincrease battery life. To achieve both linearity and efficiency, socalled linearisation techniques are used to improve the linearity of themore efficient amplifier classes, for example class ‘AB’, ‘B’ or ‘C’amplifiers. A number and variety of linearising techniques exist, whichare often used in designing linear transmitters, such as CartesianFeedback, Feed-forward, and Adaptive Pre-distortion.

Voltages at the output of the linear, e.g. Class AB, amplifier aretypically set by the requirements of the final RF power amplifier (PA)device. Generally, the minimum voltage of the PA is significantly largerthan that required by the output devices of the Class AB amplifier.Hence, they are not the most efficient of amplification techniques. Theefficiency of the transmitter (primarily the PA) is determined by thevoltage across the output devices, as well as any excess voltage acrossany pull-down device components due to the minimum supply voltage (Vmin)requirement of the PA.

In order to increase the bit rate used in transmit uplink communicationchannels, larger constellation modulation schemes, with an amplitudemodulation (AM) component are being investigated and, indeed, becomingrequired. These modulation schemes, such as sixteen-bit quadratureamplitude modulation (16-QAM), require linear PAs and are associatedwith high ‘crest’ factors (i.e. a degree of fluctuation) of themodulation envelope waveform. This is in contrast to the previouslyoften-used constant envelope modulation schemes and can result insignificant reduction in power efficiency and linearity.

To help overcome such efficiency and linearity issues a number ofsolutions have been proposed. One technique used relates to modulatingthe PA supply voltage to match the envelope of the radio frequencywaveform being transmitted by the RF PA. Envelope modulation requires afeedback signal from the PA supply to one of the control ports of theamplifier. Proposed solutions that utilise envelope modulation includeenvelope elimination and restoration (EER), and envelope tracking (ET).Both of these approaches require the application of a wideband supplysignal to the supply port of the PA.

It is known that the use of PA supply RF envelope tracking may improveboth PA efficiency and linearity for high peak-to-average power (PAPR)high power transmit conditions. FIG. 1 illustrates a graphicalrepresentation 100 of two alternative techniques; a first technique thatprovides a fixed voltage supply 105 to a PA, and a second techniquewhereby the PA supply voltage is modulated to track the RF envelopewaveform 115. In the fixed supply case, excess PA supply voltageheadroom 110 is used (and thereby potentially wasted), irrespective ofthe nature of the modulated RF waveform being amplified. However, forexample in the PA supply voltage tracking of the RF modulated envelopecase 115, excess PA supply voltage headroom can be reduced 120 bymodulating the RF PA supply, thereby enabling the PA supply toaccurately track the instant RF envelope.

It is known that switched-mode power supply (SMPS) techniques may beused to provide improved efficiency. A SMPS is an electronic powersupply that incorporates a switching regulator in order to be highlyefficient in the conversion of electrical power. Like other types ofpower supplies, an SMPS transfers power from a source, such as a batteryof a wireless communication unit, to a load, such as a power amplifiermodule, whilst converting voltage and current characteristics. An SMPSis usually employed to efficiently provide a regulated output voltage,typically at a level different from the input voltage. Unlike a linearpower supply, the pass transistor of a switching mode supply switchesvery quickly between full-on and full-off states, which minimize wastedenergy. Voltage regulation is provided by varying the ratio of ‘on’ to‘off’ time. In contrast, a linear power supply must dissipate the excessvoltage to regulate the output. This higher efficiency is the primaryadvantage of a switched-mode power supply. Switching regulators are usedas replacements for the linear regulators when higher efficiency,smaller size or lighter weight power supplies are required. They are,however, more complicated, their switching currents can cause electricalnoise problems if not carefully suppressed, and simple designs may havea poor power factor.

FIG. 2 illustrates graphically 200 output power 205 versus input power210, various functional and operational advantages that can be achievedwhen a PA supply (drain) voltage is modulated to use an envelopetracking technique. By enabling the PA (drain) supply voltage to trackthe instant RF envelope 115, the PA may be kept in modest compression atconstant gain 215 over the range of the amplitude modulation toamplitude modulation (AM-AM) curves 220. Such tracking of the supplyvoltage of the instant RF envelope 115 enables a higher output powercapability 225 for the same linearity (using envelope tracking) to beachieved by the transmitter, as compared to techniques that do not allowthe PA supply voltage to track the instant RF envelope of the PA. Inaddition, the envelope tracking graph 200 may also be viewed as beingable to support a PA gain reduction when employing ET 230, as comparedto an architecture that considers PA gain with a fixed supply. A skilledartisan will appreciate that this is predominantly a consequence of PAcharacteristics together with a function of the operation point of thePA under the chosen operating conditions for envelope tracking.

Thus, and advantageously, the gain of the PA that may be achieved whenenvelope tracking is implemented may be reduced 230 as compared to thePA gain that uses a fixed PA supply voltage. Envelope tracking may alsosupport a high efficiency gain potential for high PAPR conditions. Inaddition, the PA may operate at a cooler temperature for the same outputpower, thereby reducing heat loss and increasing efficiency. However, itis also known that envelope tracking requires a high efficiency, highbandwidth supply modulator and accurate tracking of the RF envelope istherefore difficult to achieve in practical implementations.

FIG. 3 illustrates graphically 300 envelope spectral density 305 versusfrequency 310 required when a PA supply (drain) voltage is modulatedusing an envelope tracking technique. FIG. 3 further illustratesgraphically 350 a corresponding integrated amplitude modulated power 355versus frequency 360. Envelope spectral density exhibits a number ofcommon features for different modulation cases, for example, alow-frequency region, which contains the majority of the energy, and ahigh-frequency region, which must be reproduced up to, say, 4-8 MHz. Asillustrated, the two energy regions are separated by a region, coveringa range of roughly 10 kHz-400 kHz, which contains little energy.

Thus, a need exists for improved power supply integrated circuits,wireless communication units and methods for power amplifier supplyvoltage control that use such linear and efficient transmitterarchitectures, and in particular a wideband power supply architecturethat can provide a supply voltage in a power efficient manner.

SUMMARY OF THE INVENTION

Accordingly, the invention seeks to mitigate, alleviate or eliminate oneor more of the above mentioned disadvantages, either singly or in anycombination. Aspects of the invention provide an integrated circuit anda wireless communication unit as described in the appended claims.

These and other aspects of the invention will be apparent from, andelucidated with reference to, the embodiments described hereinafter.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, aspects and embodiments of the invention will bedescribed, byway of example only, with reference to the drawings.Elements in the figures are illustrated for simplicity and clarity andhave not necessarily been drawn to scale. Like reference numerals havebeen included in the respective drawings to ease understanding.

FIG. 1 illustrates a graphical representation of a first power supplytechnique that provides a fixed voltage supply to a PA, and a secondpower supply technique whereby the PA supply voltage is modulated totrack the RF envelope.

FIG. 2 illustrates graphically various functional and operationaladvantages that can be achieved when a PA supply (drain) voltage ismodulated to use an envelope tracking technique.

FIG. 3 illustrates graphically a power spectral density versus frequencywhen a PA supply (drain) voltage is modulated to use an envelopetracking technique.

FIG. 4 illustrates an example block diagram of a wireless communicationunit adapted to support envelope tracking.

FIG. 5 illustrates one example block diagram of a part of a power supplycircuit of a transmitter chain of a wireless communication unit adaptedto support envelope tracking.

FIG. 6 illustrates a further example block diagram of a part of a powersupply circuit of a transmitter chain of a wireless communication unitadapted to support envelope tracking.

FIG. 7 illustrates an example timing diagram of a power supply circuitof a transmitter chain of a wireless communication unit adapted tosupport both envelope tracking and fixed drain.

FIG. 8 illustrates a yet further example block diagram of a part of apower supply circuit of a transmitter chain of a wireless communicationunit adapted to support envelope tracking.

FIG. 9 illustrates a still further example block diagram of a part of apower supply circuit of a transmitter chain of a wireless communicationunit adapted to support envelope tracking.

FIG. 10 illustrates a yet still further example block diagram of a partof a power supply circuit of a transmitter chain of a wirelesscommunication unit adapted to support envelope tracking.

FIG. 11 illustrates a yet still even further example block diagram of apart of a power supply circuit of a transmitter chain of a wirelesscommunication unit adapted to support envelope tracking.

FIG. 12 illustrates a yet still even further example block diagram of apart of a power supply circuit of a transmitter chain of a wirelesscommunication unit adapted to support envelope tracking.

FIG. 13 illustrates a yet still even further example block diagram of apart of a power supply circuit of a transmitter chain of a wirelesscommunication unit adapted to support envelope tracking.

FIG. 14 illustrates a yet still even further example block diagram of apart of a power supply circuit of a transmitter chain of a wirelesscommunication unit adapted to support envelope tracking.

FIG. 15 illustrates an example flowchart for envelope tracking.

FIG. 16 illustrates a typical computing system that may be employed toimplement signal processing functionality in embodiments of theinvention.

DETAILED DESCRIPTION

Examples of the invention will be described in terms of one or moreintegrated circuits for use in a wireless communication unit, such asuser equipment in third generation partnership project (3GPP™) parlance.However, it will be appreciated by a skilled artisan that the inventiveconcept herein described may be embodied in any type of integratedcircuit, wireless communication unit or wireless transmitter that couldbenefit from improved linearity and efficiency. In some describedexamples of the invention, a power supply for a power amplifier, forexample as part of a linear transmitter, has been adapted to support awideband power supply that may provide improved linearity and efficiencyto an RF PA. Although examples of the invention have been described withrespect to an envelope tracking design, it is envisaged that theinvention may be implemented in any transmitter architecture.

Furthermore, although examples of the invention have been described withrespect to transmission of predominantly amplitude modulated waveforms,it is envisaged that the invention may be implemented with any waveformstructures, particularly where the majority of the energy is located atfrequencies close to DC.

In addition, although examples of the invention have been described withrespect to a wideband linear transmitter architecture, as the efficiencybenefits are most relevant to wideband systems with specific propertiesthat allow the benefits of using efficient switch mode power supplies tosupply much of the energy to be realised, it is envisaged that theinvention may be also implemented in a narrowband linear transmitterarchitecture, such as Cartesian feedback or adaptive pre-distortion.

In some examples of the invention, a number of control mechanisms is/areprovided in order to optimise a DC level of a linear amplifier (e.g.class AB amplifier) output that is used in conjunction with a switchmode power supply for a radio frequency power amplifier. With knownenvelope modulated/envelope tracking systems, the crest factor (peak toaverage ratio (PAR)) of the envelope waveform may exceed 3 dB, whereas atarget amplifier output voltage setting would be of the order of lessthan VDD/2. In some examples of the invention, the control mechanismsdescribed may have minimal or no additional overhead on current suppliedby the linear amplifier (e.g. class AB) output. Furthermore, in someexamples of the invention, the control mechanisms may have minimal or noeffect on the switch mode power supply to the radio frequency poweramplifier.

An architecture is described for providing a modulator supply, which inone example is a composite/hybrid supply comprising a switch mode and/orlower frequency part and a linear and/or higher frequency part to aradio frequency (RF) power amplifier (PA). The integrated circuitcomprises a low-frequency power supply path comprising a switchingregulator and a high-frequency power supply path, whereby in combinationthe low-frequency power supply path and high-frequency power supply pathprovide a power supply to an output port of the integrated circuit forcoupling to a load, such as in one example a supply port of the RF PA.The architecture, which in some examples may comprise one or moreintegrated circuits and/or components, further comprises an amplifiercore arranged to drive a power supply signal on the high-frequency powersupply path wherein the amplifier core comprises an input comprising avoltage feedback from the output port. In some examples, a switch modepower supply (SMPS) acts as a controlled current source where thevoltage feedback provides control of the SMPS voltage. Also this voltagefeedback loop ensures that the voltage at the load (e.g. supply port ofthe RF PA), which is a composite of the instantaneous currents from theswitched mode power supply and the amplifier interacting with theimpedance of the load (e.g. supply port of the PA), tracks the targetreference voltage. The amplifier output is AC coupled to the powersupply path. Hence, in this manner and in some example embodiments, anintegrated circuit for providing an improved linear and efficient supplyvoltage for a power amplifier, and in particular a wideband power supplyvoltage for a power amplifier, is described.

Referring first to FIG. 4, a block diagram of a wireless communicationunit (sometimes referred to as a mobile subscriber unit (MS) in thecontext of cellular communications or an user equipment (UE) in terms ofa 3^(rd) generation partnership project (3GPP™) communication system) isshown, in accordance with one example embodiment of the invention. Thewireless communication unit 400 contains an antenna 402 preferablycoupled to a duplex filter or antenna switch 404 that provides isolationbetween receive and transmit chains within the wireless communicationunit 400.

The receiver chain 410, as known in the art, includes receiver front-endcircuitry 406 (effectively providing reception, filtering andintermediate or base-band frequency conversion). The front-end circuitry406 is coupled to a signal processing function 408. An output from thesignal processing function 408 is provided to a suitable user interface430, which may encompass a screen or flat panel display. A controller414 maintains overall subscriber unit control and is coupled to thereceiver front-end circuitry 406 and the signal processing function 408(generally realised by a digital signal processor (DSP)). The controlleris also coupled to a memory device 416 that selectively stores variousoperating regimes, such as decoding/encoding functions, synchronisationpatterns, code sequences, and the like.

In accordance with examples of the invention, the memory device 416stores modulation data, and power supply data for use in supply voltagecontrol to track the envelope of the radio frequency waveform output bythe wireless communication unit 400 and processed by signal processingfunction 408. Furthermore, a timer 418 is operably coupled to thecontroller 414 to control the timing of operations (transmission orreception of time-dependent signals and in a transmit sense the timedomain variation of the PA (drain) supply voltage within the wirelesscommunication unit 400).

As regards the transmit chain, this essentially includes the userinterface 430, which may encompass a keypad or touch screen, coupled inseries via signal processing function 428 to transmitter/modulationcircuitry 422. The transmitter/modulation circuitry 422 processes inputsignals for transmission and modulates and up-converts these signals toa radio frequency (RF) signal for amplifying in the power amplifiermodule or integrated circuit 424. RF signals amplified by the PA moduleor PA integrated circuit 424 are passed to the antenna 402. Thetransmitter/modulation circuitry 422, power amplifier 424 and PA supplyvoltage module 425 are each operationally responsive to the controller414, with the PA supply voltage module 425 additionally responding to areproduction of the envelope modulated waveform from thetransmitter/modulation circuitry 422.

The signal processor function 428 in the transmit chain may beimplemented as distinct from the processor 408 in the receive chain 410.Alternatively, a single processor may be used to implement processing ofboth transmit and receive signals, as shown in FIG. 4. Clearly, thevarious components within the wireless communication unit 400 can berealised in discrete or integrated component form, with an ultimatestructure therefore being merely an application-specific or designselection.

Furthermore, in accordance with examples of the invention, thetransmitter/modulation circuitry 422, together with power amplifier 424,PA supply voltage 425, memory device 416, timer function 418 andcontroller 414 have been adapted to generate a power supply to beapplied to the PA 424. For example, a power supply is generated that issuitable for a wideband linear power amplifier, and configured to trackthe envelope waveform applied to the PA 424.

Referring now to FIG. 5, one generic example block diagram of a part ofa power supply circuit 500 of a transmitter chain of a wirelesscommunication unit is illustrated, for example the wirelesscommunication unit of FIG. 4. The power supply circuit 500 in FIG. 5 hasbeen configured and/or adapted to support envelope tracking. A poweramplifier (PA) 424 receives an envelope modulated RF signal 502 as aninput RF signal to be amplified. The PA 424 amplifies the RF signal andoutputs an amplified envelope modulated RF signal to an antenna 402. ThePA 424 receives a power supply from a power supply integrated circuit520, as illustrated. A power source, such as battery 508, is operablycoupled to a low-frequency-path supply module 518 in the power supplyintegrated circuit 520, which in one example is arranged to supply alow-frequency current 534, as part of a power supply to the PA 424, in ahighly efficient manner.

The battery 508 is also operably coupled to a high-frequency-path supplymodule 506, which in one example is arranged to provide a voltagesupply, such as a switch mode power supply, to a linear amplifier 504 ina highly efficient manner. In an alternative example, thehigh-frequency-path supply module 506 may be by-passed, such that thelinear amplifier 504 is supplied directly from the power source, e.g.battery 508. The linear amplifier 504 receives, as a first input, anenvelope signal 503 that is arranged to track the envelope of the RFsignal 502 that is input to the PA 424. The linear amplifier 504comprises a second input that receives voltage feedback 510 of thevoltage 528 applied to the PA 424, which is used to control the voltageat the load (e.g. power supply port of the PA 424).

The low-frequency-path supply module 518 receives, as an input, avoltage feedback signal 514 coupled from the output 512 of the linearamplifier 504. The output 512 from the linear amplifier 504 is alsocoupled to the voltage at the power supply port of the PA 424 through acapacitor 533. The linear amplifier 504, which in one example is of aclass-AB configuration, provides power supply signal energy to an outputof the power supply IC 520 that is not supplied by the low-frequencysupply module 518.

In one example circuit, within the low-frequency-path supply module 518there exists an error amplifier 529. The error amplifier 529 comparesthe voltage feedback signal 514 to a reference voltage 530, and producesan error voltage 531. In some examples, the error amplifier 529 alsoincludes frequency compensation to ensure stability of the feedbackloop. In one possible example, the frequency compensation may have anintegrating characteristic, such that the time-averaged differencebetween the reference voltage 530 and the sense voltage 514 is driven tozero. The unity-gain bandwidth of the integrator may be constrained tobe lower in frequency than other dynamic elements of the feedback loop,so as to ensure stability. In alternative examples, it is envisaged thatother frequency compensation techniques used in switching regulators mayalso be used. In this manner, the error voltage 531 acts as an input toa pulsewidth modulator 532, which provides a low-frequency current 534to the inductor 515. This arrangement is commonly used in switchingregulators. In one example, the pulsewidth modulator 532 operates bycomparing the error voltage 531 to a periodic triangular waveform offixed ramp rate. The output of this comparison is a pulsewidth-modulatedsignal that can be used to generate the low-frequency current 534.

In a steady state condition, the low-frequency current 534 that isapplied to the power supply port of the PA 424 may be arranged to besufficient to provide the DC current, whilst the linear amplifier 504sources the AC current. In this manner, the use of a voltage sensearrangement, as described, facilitates monitoring the output voltage 512of the linear amplifier 504. The low-frequency-path supply module actsto maintain the output voltage 512 of the linear amplifier at such alevel that the amplifier operates within its designed output voltagerange. It does so by varying the level of output current 534 provided.Current sensing may be used in some examples to improve the response ofthe switching regulator. Hence, the linear amplifier 504 is suppliedfrom a second switch mode power supply (SMPS), namely thehigh-frequency-path supply module 506, with the output of the linearamplifier 504 AC coupled (via the high-frequency path coupling element533) to the output feeding the load (namely the power supply port of thePA 424).

Advantageously, AC coupling of the high-frequency power supply signal tothe output port of the IC 520 using the coupling capacitor 533 allowsthe quiescent voltage operating point at the output of the linearamplifier 504 to be decoupled from the supply requirements of the poweramplifier 424, thereby taking advantage of the differences in thevoltage compliance requirements of the linear amplifier 504 and thepower amplifier 424.

In order to better appreciate the operation of FIG. 5, let us considerthat the ac-coupling capacitor 533 stores a fixed charge, resulting in afixed voltage Vcap and that the low-frequency path is inactive. If thelinear amplifier 504 has an output voltage Vamp, then the supply voltageto the PA will be Vamp+Vcap. If the output voltage of the linearamplifier 504 has an average value Vampdc and a time-varying valueVampac, then the supply voltage to the PA 424 will be:

Vampdc+Vampac+Vcap.

Thus the average value of the supply voltage to the PA 424 will beVcap+Vampdc, its maximum value will be Vcap+Vampdc plus the maximumvalue of Vampac, and its minimum value will be Vcap+Vampdc plus theminimum value of Vampac.

By selecting an appropriate value for the level shifting voltage Vcap,it is possible to reduce the supply voltage to the linear amplifier 504such that it is just sufficient to supply a full range of an ac voltageswing on the PA supply, as well as allow the capacitor 533 add enoughvoltage to provide the correct average voltage on the PA supply.Minimizing the supply voltage to the linear amplifier in this way alsominimizes power dissipation in the supply modulator 520. For this schemeto function properly in a real circuit, the LF supply 518 should beconfigured to maintain the proper voltage across the ac couplingcapacitor. Further examples are illustrated in later figures detailinghow this can be achieved.

The example in FIG. 5 uses a control loop, sensing the voltage at theoutput voltage of the linear amplifier 504, to control the current ofthe main SMPS. In this example arrangement, the voltage across the ACcoupling capacitor is determined by the voltage sense at the output ofthe linear amplifier 504, which is then compared with a target voltage,together with a voltage sensed at the PA load, which is fed back to the(differential) linear amplifier 504 where it is compared with theenvelope reference signal 503.

When a SMPS is used to supply the linear amplifier 504, this reducedvoltage supply requirement for the linear amplifier 504 requires a lowercurrent draw from the main energy source e.g. battery 508, as comparedto a case when it is directly coupled to the PA load, thereby resultingin an overall efficiency improvement. In some examples, andadvantageously, the target amplifier output voltage can be adjusted fordifferent output power levels and transmission modulation schemes, inorder to optimise the amplifier supply requirements.

The generic example block diagram of FIG. 5 comprises at least thefollowing common circuit elements or components that are replicated inthe example embodiments of FIGS. 6-10: a low-frequency power pathimplemented for example with a switching regulator; a high-frequencypower supply path driven by an amplifier, such as a linear amplifier 504exhibits, say, a Class AB mode of operation; voltage feedback 514 fromthe output of the linear amplifier 504 to the switching regulator of thelow-frequency power supply path 518; a voltage feedback 510 from the PAsupply voltage 528 to the linear (e.g. Class AB) amplifier 504; and acapacitor 533 (and in some examples inductor 515) that couples thehigh-frequency and low-frequency power supply paths together. By usingthe capacitor 533 (and in some examples inductor 515), it is possible tocombine power at dc and low frequencies from the switching regulator 518with higher-frequency ac power from the linear amplifier 504.

Thus, FIG. 5 illustrates a means for implementing a wideband powersupply in a power efficient manner. The power supply is configured toprovide power to a load, such as a power supply for a RF Power Amplifier(PA), and in particular an envelope tracking supply that may achievehigh efficiency when driving PAs of differing load characteristics. Thepower supply may also, and advantageously, be configured to providesupply envelopes corresponding to different modulation formats.

Referring now to FIG. 6, a more detailed example block diagram of a partof a power supply circuit 600 of a transmitter chain of a wirelesscommunication unit, adapted to support envelope tracking, isillustrated. The operation of elements described with reference to FIG.5, with like reference numerals used, is not replicated in describingFIG. 6 in order to ease understanding. The battery andhigh-frequency-path supply are used in the same way in FIG. 6 as in FIG.5, but their symbols have been removed from FIG. 6 for clarity. In FIG.6, an envelope voltage 602 is input to an envelope conditioning module603. The envelope conditioning module 603 is arranged to modify andlimit the envelope signal characteristics, which in some examples mayinvolve one or more of a number of actions, for example:

-   -   (i) limiting a minimum value of the power supply to meet        requirements of the PA    -   (ii) reducing the peak-to-peak voltage of the envelope signal        improving efficiency,    -   (iii) restricting the signal bandwidth of the envelope signal,    -   (iv) performing any necessary gain and offset alignment of the        envelope signal; and    -   (v) implementing any signal formatting, such as converting        between differential and single ended representation.

The inventors have identified that an envelope tracking supply haslimited benefits when lower output levels are used, or certainmodulation schemes are used with reduced AC content leading to lower PARenvelope waveforms. For such low output levels and/or modulationschemes, the DC voltage applied to the PA has a greater significancewith the power of the AC content of the envelope significantly reduced,negating the benefits of envelope tracking and the efficiencyperformance gain is reduced. Therefore, in these scenarios, a fixeddrain (FD) mode of operation is able to take full advantage of the fullswitching supply. Although the application of the DC components and ACcomponents is described with reference to FIG. 6, it is envisaged thatsuch application is common to a number of the other described exampleembodiments.

Thus, in some examples of the invention, two modes of operation aresupported, namely an envelope tracking (ET) mode and a fixed drain (FD)mode. The selection of the mode to be used in providing the power supplyto the PA is performed by mode control module 616.

ET Mode:

In ET mode, the PA power supply is a time varying signal, which tracksthe required signal envelope, in order to achieve the efficiencybenefits discussed.

There are at least two operational factors that favour use of ET mode,namely high crest factor signals (i.e. where the peak-to-average ratioof the envelope signal is high) and higher output power levels, whereasthe minimum voltage requirement of the PA and the power overhead of theAC path (including the quiescent power of the amplifier) is lessimportant. Hence, in one example, the benefit of the mode control module616 setting the power supply to an ET mode of operation is greatest forsignals using modulation schemes that result in high crest factor powerenvelope signals, for the upper section of the output power range.

In both the ET mode and the FD mode, the power supply system has toprovide the full power spectrum, i.e. both high-frequency andlow-frequency energy. Both the ET mode and the FD mode use a switch modepower supply (SMPS) arrangement in order to supply the low-frequencypower. However, the two modes of operation differ in how they handle thehigh-frequency requirements.

In ET mode, the switch 614 is configured as ‘open’, the linear amplifier504 and high-frequency-path supply module 506 are enabled, and the (ET-)sense feedback input 514 if the low-frequency-path supply module 518 isselected. The linear amplifier 504 operates in voltage feedback to forcethe output voltage 528 to be substantially equal to the conditionedenvelope voltage 503. The ET-sense feedback voltage 514 may then becompared to a reference voltage, which in one example is generated usinga digital-to-analog converter (DAC) (not shown).

Thus, in this manner in the ET mode, the AC coupling capacitor 533performs a function of a dc level shifter and the high-frequency poweris provided by the linear amplifier 504. Using this active path for thehigh-frequency power allows the output power supply to track the RFenvelope (see FIG. 1 image 120), which limits the power dissipated inthe PA 424. However, in ET mode, the power dissipation in the powersupply module may be larger because the high-frequency-path power supply506 and the linear amplifier 504 must be powered on.

In ET mode, the circuit of FIG. 6 may be operated such that there isalways a positive charge, for example the voltage at the output 528 isgreater than voltage at the output of the amplifier 512, stored on thecapacitor 533. In this manner, it is possible for the output voltage 528to exceed the output range of the linear amplifier 504. The power supplyproduced by the high-frequency-path power supply 506 need be only ofsufficient voltage to sustain the ac amplitude of the envelope voltage602. In this way, the power dissipated within the linear amplifier canbe minimized.

The voltage feedback loop, which includes the inverting stage 625 andthe low-frequency-path power supply 518, ensures that the average outputvoltage of the linear amplifier 504 and the voltage across the couplingcapacitor 533 are maintained at the appropriate levels. The invertingstage 625 produces a complementary signal to the linear amplifier outputvoltage 512. The feedback voltage 514 is then passed through the analogmultiplexer 628, which is used to select between ET and FD modes. Theoutput of the analog multiplexer 628 is then compared to a referencevoltage 530 in error amplifier 529, and the resulting error voltage Verr531 is generated.

As in FD mode, the error amplifier 529 contains compensation tostabilize the loop. The compensation has a low-pass characteristic,which helps to filter out high-frequency information present in thefeedback voltage 514. Also as in FD mode, the pulsewidth modulatorformed by the comparator 630 and ramp voltage 631 produces a pulsewidthmodulated power output 627. This power output is filtered by inductor622 to provide a roughly constant current to the output 528. In someexamples, the inductor 622 and capacitor 533 form a low-pass filter,which is configured to locate a double pole in a low energy range of apower spectral density of the reference signal 530. In this manner, thefeedback loop acts in such a way as to maintain the average amplifieroutput voltage 512 equal to the reference voltage REF 530.

FD Mode:

In FD mode, switch 614 is configured as ‘closed’, the linear amplifier504 and high-frequency-path supply module 506 are disabled, and the(FD-) sense feedback input 629 of the low-frequency-path power supply isselected. In FD mode, the output 512 from the linear amplifier 504 iscoupled to a fixed drain (FD) mode switch 614, which in a closedconfiguration (as set, for example by mode control module 616) groundsthe output from the linear amplifier 504. In this FD mode, the PA powersupply is fixed at the minimum voltage requirement (of the PA 424) inorder to support the transmitted envelope waveform, for example for atime period between power level updates.

In the FD mode, the power supply may be re-configured to use the ACcoupling capacitor 533 as a filtering element for the DC-DC SMPS. Inthis manner, the AC coupling capacitor 533 provides the high-frequencypower required by the PA. In FD mode, the linear amplifier andhigh-frequency-path regulator may be disabled to save power. The PAsupply voltage 528 is at a higher level in FD mode (see FIG. 1 image110), but the quiescent current of the power supply is lower.

In some examples, the operation of the circuit in FD mode resembles aconventional voltage-mode buck regulator. The FD-sense feedback voltage629 passes through an analog multiplexer. The FD-sense feedback voltage629 is then compared to a reference voltage REF 530, which in oneexample is generated using a digital-to-analog converter (DAC) (notshown). The difference between the FD-sense feedback voltage 629 andvoltage REF 530 is amplified by the differential error amplifier 529,which includes frequency compensation for loop stability. The resultingerror voltage Verr 531 is compared to a ramp voltage 631 by comparator630.

In some examples, the comparator 630 may be reset at, say, a fixedperiodic rate by a clock signal, thereby producing a rising edge at afixed rate, whilst the falling edge is determined, for example, by theoutput of the comparator 630, thereby producing a pulse wave modulated(PWM) power output 627. In some examples, the PWM power output may thenbe filtered by, say, inductor 622 and coupling capacitor 533 in order toremove high frequency components and produce the output power supply528. The feedback loop acts to maintain the voltage at the output 528that may be equal to the input reference signal REF 530. Thisconfiguration is commonly used in switched-mode power supplies and isknown as ‘voltage-mode’ control.

As an alternative to PWM modulation, any of a number of well-knownmodulation schemes that convert a control voltage to a duty cycle may beused.

Transition Between ET Mode and FD Mode:

A particular feature of the more detailed example block diagram of apart of a power supply circuit 600 of FIG. 6 is that it supports atransition from FD mode in a first (e.g. n−1) time slot 705 to ET modein a second (e.g. n) time slot 710 and thereafter from ET mode in thesecond (e.g. n) time slot 710 to FD mode in a third (e.g. n+1) time slot715, as illustrated in the example timing diagram 700 of FIG. 7. Thearchitecture shown in FIG. 6 ensures a speedy transition with a minimumof disruption to the power supply output 528. The same error voltageVerr 531 is used in both FD mode and in ET mode, which ensures that noabrupt changes in duty cycle are observed during a mode transition. Whentransitioning from FD mode in a first (e.g. n−1) time slot 705 to ETmode in a second (e.g. n) time slot 710, it is desirable that theamplifier output 512 of linear amplifier 504 makes a gradual transitionfrom ground to its final modulated voltage. In order to ensure this,during the transition from FD mode in a first (e.g. n−1) time slot 705to ET mode in a second (e.g. n) time slot 710, the dc and ac values ofthe conditioned envelope voltage 503 are gradually ramped up from zerovolts 720 to their final values 725. Conversely, when making atransition from ET mode in the second (e.g. n) time slot 710 to FD modein a third (e.g. n+1) time slot 715, the dc and ac values of theconditioned envelope voltage 503 are gradually decreased from theirsteady-state values 725 to zero volts 720. Through use of such rampedand tapered envelope signals, abrupt disturbances to the control loopcan be eliminated, thereby keeping the power supply within regulationthroughout the transition, as illustrated in FIG. 7.

FIG. 8 illustrates a yet further example block diagram 800 of a part ofa power supply circuit of a transmitter chain of a wirelesscommunication unit adapted to support envelope tracking. The yet furtherexample of FIG. 8 highlights an alternative way of controlling thelow-frequency-path supply 518. For ease of understanding, and not toobfuscate or distract from the description of FIG. 8, electroniccomponents and circuits of the transmitter chain described withreference to earlier figures will not be explained again in any greaterextent than that considered necessary.

It is contemplated that any of a number of control methods may be usedin the low-frequency-path power supply 518, both in FD mode and in ETmode in various example embodiments of the invention. For example, thewell-known voltage-mode control approach may be used, as shown in FIG.6. In the example of FIG. 8, a current-mode feedback control loopincluding elements 801, 802 and 630 is used. Current-mode control is awell-known method used in switching regulators, in which the currentthrough the inductor is sensed and feedback control applied to stabilizeit. A voltage feedback loop is also used to regulate the output voltage,just as in a voltage-mode controller. The ET voltage feedback loopconsists of elements 512, 625, 514, 628, 529, 531, 630, 622. The FDvoltage feedback loop includes elements 629, 628, 529, 531, 630, 622.The advantages of adding the current loop include simpler compensationmethods required for the voltage loop as well as a faster response tocertain types of transient disturbances.

In the example of FIG. 8, a conventional current-mode switched modepower supply is used as the low-frequency-path supply. A current sensor801 monitors the instantaneous current in the inductor 622. The currentis converted to a voltage by the current-to-voltage converter 802. Theresulting voltage is used as the ramp voltage 631, which is compared tothe error voltage 531 by the comparator 630. This feedback loop operatesin both FD and ET modes, just as in the circuit of FIG. 6.

FIG. 9 illustrates a still further example block diagram 900 of a partof a power supply circuit of a transmitter chain of a wirelesscommunication unit adapted to support envelope tracking. The yet furtherexample of FIG. 9 highlights an alternate method of realizingcurrent-mode feedback. For ease of understanding, and not to obfuscateor distract from the description of FIG. 9, electronic components andcircuits of the transmitter chain described with reference to earlierfigures will not be explained in any greater extent than that considerednecessary.

In the circuit of FIG. 9, the low-frequency-path power supply 518 hastwo current-sense feedback inputs. In addition to the inductor currentsensor 801 there is a current sensor 901 at the output of the linearamplifier 504. A second analog multiplexer 902 is arranged to selectbetween the two current-sense feedback inputs and passes the selectedinput through to the current-to-voltage converter 802. The current-sense801 from the low-frequency-path supply is used in FD mode, as in FIG. 8.In ET mode, the amplifier current sensor 901 is used. The output currentof the linear amplifier 504 contains high-frequency information aboutthe instantaneous current drawn by the PA 424, because the amplifiersupplies this high-frequency current. Using this configuration,information about the current demands of the PA 424 can be fed backthrough the current loop of the SMPS, which has much higher bandwidththan the voltage loop. This implies that, using the circuit of FIG. 9,the low-frequency-path voltage regulator can potentially respond fasterto the demands of the PA.

FIG. 10 illustrates a yet still further example block diagram 1000 of apart of a power supply circuit for a PA of a transmitter chain of awireless communication unit adapted to support envelope tracking. Forease of understanding, and not to obfuscate or distract from thedescription of FIG. 10, electronic components and circuits of thetransmitter chain described with reference to earlier figures will notbe explained in any greater extent than that considered necessary.

The output 503 from the envelope conditioning module 603 is input to thelinear amplifier 1004. In FIG. 10, the devices that comprise the outputstage of the linear amplifier 1004 are shown explicitly as n-channeltransistor 1001 and p-channel transistor 1002. This example of FIG. 10does not include a discrete switch to ground the bottom plate of thecoupling capacitor 627 in FD mode. Instead, the output devices (namelyn-channel transistor 1001 and p-channel transistor 1002) of the linearamplifier 1004 can be configured in two ways. In ET mode, these twotransistors/devices operate as part of the linear amplifier 1004. In FDmode, the n-channel transistor 1001 is switched on and the p-channeltransistor 1002 is switched off. In this way, the output of the linearamplifier 1004 is strongly coupled to ground, thereby emulating theswitch of earlier examples. Although this example is described in termsof switching to ground via n-channel transistor 1001 (e.g. an nMOSswitch), a more general case may be to switch to a DC voltage, whichcould be a supply voltage, in which case the p-channel transistor 1002could be used. By encompassing the amplification and ground switchingfunctions in a single element, the complexity of the circuit can beadvantageously reduced.

In one alternative implementation, the NMOS device(s) of the linearamplifier 1004 may be used together with a supplementary switch (notshown), in order to use and benefit from a combination of both methodsand architecture of FIG. 8 and FIG. 10.

FIG. 11 illustrates a yet still even further example block diagram 1100of a part of a power supply circuit for a PA of a transmitter chain of awireless communication unit, adapted to support envelope tracking. Theexample of FIG. 11 illustrates an alternate way to implement the controlloop for ET mode in which the FD control loop and ET control loop arelargely independent of each other. In some examples, this may beadvantageous if different characteristics are desired for the twocontrol loops. For ease of understanding, and not to obfuscate ordistract from the description of FIG. 11, electronic components andcircuits of the transmitter chain described with reference to earlierfigures will not be explained in any greater extent than that considerednecessary.

The ET mode control loop of the circuit of FIG. 11 contains aproportional integral (PI) controller 1101 that is independent from thelow-frequency-path regulator. Within the PI controller 1101 there is acurrent-voltage (I/V) converter 1102 that converts the currentinformation from current sensor 901 into a voltage. There is also adifference amplifier 1103 that amplifies the difference between theoutput voltage 512 of the linear amplifier 504 and a reference voltageREF_ET 1104. The reference voltage REF_ET 1104 represents the desiredaverage output voltage 512 of the linear amplifier 504. The output ofthe difference amplifier 1103 is integrated by the integrator 1105. Thedifference between the output voltage of the integrator 1105 and that ofthe I/V converter 1102 is then computed by the summation circuit 1106.

The output voltage 1110 of the summation circuit 1106 represents theinstantaneous current at the output of the linear amplifier 504, plus aslowly-varying term that reflects the integrated difference between theoutput voltage 512 of the linear amplifier 504 and its desired value1104. As such, the output voltage 1110 can be used directly as thecontrol voltage to a pulsewidth modulator in order to produce theappropriate current to apply to the coupling network. The analogmultiplexer 1107 passes this voltage 1110 through to the comparator 630,which compares it to a fixed voltage THR_ET, passed through analogmultiplexer 1109.

Thus, it can be seen that the comparator 630 compares a differencebetween the two inputs 531, 631 in order to stablize the loop. Inessence:

-   -   Input signal 631−Input signal 531=Viab−Avg        (Vabout−REF_ET)−THR_ET

Where: Viab is the current sensing output of I/V convertor 1102; and,

Vabout means class AB output 512 of the linear amplifier 504.

The voltage at THR_ET can be chosen to null out any offsets in thecontrol loop, for example a finite offset resulting from the currentripple through the inductor 622. The resulting PWM waveform is used tocontrol the current through the inductor 622, as in the other exampleembodiments.

In closed-loop operation, the ET mode control loop tends to force theaverage output voltage 512 of the linear amplifier 504 to be equal tothe desired value 1104. It also tends to force the instantaneous outputcurrent of the linear amplifier to zero by supplying more currentthrough the low-frequency path when the output current of the linearamplifier is high.

The FD mode control loop of the circuit of FIG. 11 operates the same asin FIG. 8. The only difference is the location in the circuit of theanalog multiplexers 1107 and 1109.

In such ET architectures, the integrity of the peaks of the envelopewaveform must be maintained, whereas the integrity of the troughs of theenvelope waveform is not critical, provided sufficient voltage headroomis maintained. The troughs of the waveform are associated with a highvoltage slew rate. Therefore, in some examples of the invention, themodulated power supply 528 provided to the PA 424 may be referenced to amodified envelope waveform, with the troughs of the envelope waveformclipped or removed, i.e. the depths of the envelope waveform troughs arereduced. Removing the troughs reduces the high-frequency components fromthe voltage waveform, whilst increasing the DC content of the voltagewaveform. This concept will be hereinafter termed ‘de-troughing’.

The envelope waveform troughs correspond to the periods of minimumoutput power from PA 424 and, thus, the clipping or removal(de-troughing) of the troughs of the envelope waveform has minimal (orat least reduced) impact on overall PA power dissipation. In effect, theoperating region of the PA 424 results in the PA 424 exhibitingcharacteristics of a current sink rather than a resistor, with thecurrent being a function of the instantaneous power. The power drawn bythe linear amplifier 504 will be I_(ac)V_(amp) where V_(amp) is theamplifier supply voltage.

De-troughing increases the power dissipated by the PA 424, since thecurrent supplied to the PA 424 is essentially the same, but where thevoltage at the supply port of the PA is increased. However, sincede-troughing is applied at the points of lowest output power, the impactis minimal. De-troughing the reference waveform also reduces thepeak-to-peak voltage associated with the high frequency path, therebyreducing the amplifier supply requirements and improving the overallefficiency via the use of a second SMPS.

Thus, and advantageously in an AC coupled architecture as illustrated,de-troughing a waveform has the effect of reducing the peak-to-peakvalue (AC content), whilst increasing the DC value, and thereby thesupply requirement of the linear amplifier 504 is reduced. In effect,additional efficiency in PA power supply may be achieved from theincreased efficiency of the low-frequency supply path, as the reductionin voltage supplied from the high-frequency supply amplifier has beeneffectively, and favourably traded for increased low-frequency energyfrom the more efficient SMPS.

In one example embodiment, the envelope signal 602 applied to the linearamplifier 504 may be pre-conditioned by de-troughing, in order to reducethe envelope signal headroom with little or minimal impact on the RFperformance of the PA 424. In some examples, the pre-conditioning byde-troughing may involve a procedure as simple as limiting a minimumvalue of the reference waveform to a fixed value, such as the minimumvoltage requirement of the PA load. Alternatively, in other examples,the minimum value may be related to the average or rms value of theenvelope waveform (e.g. 9 dB below the rms value). In one exampleembodiment, the de-troughing of the envelope signal 602 applied to thelinear amplifier 504 may be additionally pre-conditioned by, sayfiltering.

In some implementations, the use of PI controller 1101 in FIG. 11 mayexhibit a low pass filter response that may introduce an additionaldelay to the control loop control. The additional delay may be as aresult of an extra low frequency pole introduced into the feedback paththrough use of PI controller 1101, which may also affect the phasemargin in the circuit's transient response. In this situation, oneexample solution is to extract and lock the dc operating point of linearamplifier 504, as illustrated in the example architecture of FIG. 12.

Therefore, FIG. 12 illustrates a yet still even further example blockdiagram 1200 of a part of a power supply circuit for a PA of atransmitter chain of a wireless communication unit, adapted to supportenvelope tracking. In this example, an envelope tracking moduleintegrated circuit 1205 is illustrated, with a selected portion ofinput/output/control pins. A skilled artisan will appreciate that thesame IC arrangement with the illustrated components and functions can beapplied to the previous architecture drawings.

In ET mode, the second switch mode power supply (SMPS), namely thehigh-frequency-path supply module 1206 supplies power to linearamplifier 504. The output of the linear amplifier 504 is AC coupled (viathe high-frequency path coupling element 1233) to the output feeding theload (namely the power supply port of the PA 424).

In addition, the example of FIG. 12 illustrates a further alternativeway to implement the control loop for ET mode in which the FD controlloop and ET control loop are largely independent of each other. In someexamples, this may be advantageous if different characteristics aredesired for the two control loops. For ease of understanding, and not toobfuscate or distract from the description of FIG. 12, electroniccomponents and circuits of the transmitter chain that have beendescribed with reference to earlier figures will not be explained in anygreater extent than that considered necessary. In contrast to the ETmode control loop of the circuit of FIG. 11 that contains a proportionalintegral (PI) controller that is independent from the low-frequency-pathregulator, the architecture of FIG. 12 illustrates a use of a subtractormodule 1220. The subtractor module 1220 subtracts the output voltage1204 of the linear class AB amplifier 504, from the modulated powersupply 528 provided to the PA 424. In the example embodiment of FIG. 12,the output 1210 from the subtractor module 1220 is added in summingjunction 1225 to a voltage representation of the output current of thelinear amplifier 504, once the output current has been converted bycurrent to voltage converter 1102.

In the example of FIG. 12, a current-mode switched mode power supply isagain used as the low-frequency-path supply, as described with referenceto FIG. 11. A current sensor 901 senses the output current of the linearamplifier 504. The output voltage 1110 of the summation circuit 1225represents the instantaneous current at the output of the linearamplifier 504, plus a slowly-varying term from low passed capacitor 1233that reflects the integrated difference between the PA supply voltage528 and the output voltage 1204 of the linear amplifier 504. As such,the output voltage 1110 can be used directly as the control voltage to apulsewidth modulator in order to produce the appropriate current toapply to the coupling network. The analog multiplexer 1107 passes thisvoltage 1110 through to the comparator 630, which compares it to a fixedvoltage THR_ET, passed through analog multiplexer 1109.

Thus, it can be seen that the comparator 630 compares a differencebetween the two inputs 531, 631 in order to stablize the loop. However,in contrast to the operation of FIG. 11, and in essence:

-   -   Input signal 631−Input signal 531=Viab+Avg        (Vout−Vabout)−THR_ET′=Viab−Avg(Vabout−REF_ET)+Avg(Vout−REF_ET)−THRET′=Viab−Avg(Vabout−REF_ET)+REF_CAP−THR_ET′=Viab−Avg(Vabout−REF_ET)+THE_ET

Where: Viab is the current sensing output of I/V convertor 1102; and,

Vout is the supply output 528 connected to PA 424;

Vabout is the output 1204 of class AB linear amplifier 504; and

REF_CAP=Avg(Vout−REF_ET) is the reference DC voltage for capacitor 1233.

THR_ET′=THR_ET+REF_CAP, while compared to THE_ET 1108 in FIG. 11.

From the above derivative, it can be seen that the circuit of FIG. 12can operate in the same manner as the circuit in FIG. 11, if THR_ET′ isset to THR_ET+REF_CAP. Namely, in closed-loop operation, the ET modecontrol loop tends to force the voltage of capacitor 1233 to be equal tothe desired REF_CAP value in FIG. 12, instead of tending to force theaverage output voltage 512 of linear amplifier 504 to be equal to thedesired REF_ET value in FIG. 11. It also tends to force theinstantaneous output current of the linear amplifier to zero bysupplying more current through the low-frequency path when the outputcurrent of the linear amplifier 504 is high as described in FIG. 11.

In effect, any low pass filtering effect provided by PI controller 1101in FIG. 11 is inherently achieved by capacitor 1233. A change of thecorner frequency of the low pass filter may be achieved via a suitableselection of the capacitance value of capacitor 1233. One advantage ofthe architecture of FIG. 12 when compared to the architecture of FIG. 11is that better phase margin may be achieved due to there being no extralow frequency pole generated within the PI controller 1101. Because theAC coupling capacitor 1233 voltage is directly used as a feedback to thecurrent-mode switched mode power supply for the low frequency path, theloop introduces no extra delay. As a consequence, loop compensation canbe more easily controlled.

The FD mode control loop of the circuit of FIG. 12 operates the same asdescribed with respect to FIG. 11.

Referring now to FIG. 13, a yet still even further example block diagram1300 of a part of a power supply circuit for a PA of a transmitter chainof a wireless communication unit, adapted to support envelope tracking,is illustrated. For ease of understanding, and not to obfuscate ordistract from the description of FIG. 13, electronic components andcircuits of the transmitter chain described with reference to earlierfigures will not be explained in any greater extent than that considerednecessary. In FIG. 13, one example control arrangement for use in thelow-frequency-path power supply 518, both in FD mode and in ET mode isdescribed. In this example, an envelope tracking module integratedcircuit 1305 is illustrated, with a selected portion ofinput/output/control pins. A skilled artisan will appreciate that thesame IC arrangement with the illustrated components and functions can beapplied to the previous architecture drawings.

In ET mode, the second switch mode power supply (SMPS), namely thehigh-frequency-path supply module 1306, supplies power to the linearamplifier 504 with the output of the linear amplifier 504 AC coupled(via the high-frequency path coupling element (e.g. capacitor 1333) tothe output feeding the load (namely the power supply port of the PA424). Notably, the example illustrated in FIG. 13 includes a pulse-widthmodulator 1336 within high-frequency-path supply module 1306 arranged toprovide a pulse-width modulated signal 1340. The pulse-width modulatedsignal 1340 is coupled to the supply 1245 of the linear amplifier 504via a filter arrangement, for example comprising inductance 1337 andcapacitance 1335 (which functions as the supply decoupling capacitor ofHF power to the linear amplifier 504). In this manner, the filteredpulse-width modulated signal 1340 is attached to the high frequencysupply 1245, thereby locking the supply voltage of Class-AB linearamplifier 504. In this manner, the class AB linear amplifier 504 issupplied by pulse-width modulated HF power, and its output delivers ACPA power to the PA 424 and being coupled to the PA via capacitor 1333.Again, when compared to the implementation of FIG. 8, it can be seenthat the inverting amplifier 625 of FIG. 8 is effectively replaced withsubtractor 1220 that extracts the DC value of coupling capacitor 1333.In this manner, the AC coupling capacitor 1333 voltage is used as afeedback to the current-mode switched mode power supply for the lowfrequency path and introduces no extra loop delay. As a consequence,loop compensation can be more easily controlled as described for FIG.12.

In FIG. 13, values for inductance 621, capacitance 1332, inductance 622,and capacitor 1333 are selected to deliver a low frequency supply powerto PA 424. Inductor 621, capacitor 1332, inductance 622 and capacitance1333 in FIG. 13 may form a 4^(th) order LC filter to further reduce anycurrent ripple due to pulse mode effects on the low frequency output. Byeffectively shorting inductance 621 and removing the effect ofcapacitance 1332, inductance 622 and capacitor 1333 in theimplementation of FIG. 13, it can be made to correspond to thecombination of inductor 622 and capacitor 1333 of FIG. 12.

In FD mode, the operation of FIG. 13 is the same as in FIG. 12, exceptthat inductor 621, capacitor 1322, inductance 622, and capacitance 1333act as a 4^(th) order low pass filter applied to the supply voltage 528of PA 424 to reduce any current ripple.

Referring now to FIG. 14, a yet still even further example block diagram1400 of a part of a power supply circuit for a PA of a transmitter chainof a wireless communication unit, adapted to support envelope tracking,is illustrated. For ease of understanding, and not to obfuscate ordistract from the description of FIG. 14, electronic components andcircuits of the transmitter chain described with reference to earlierfigures will not be explained in any greater extent than that considerednecessary. In this example, an envelope tracking module integratedcircuit 1305 is illustrated, with a selected portion ofinput/output/control pins. A skilled artisan will appreciate that thesame IC arrangement with the illustrated components and functions can beapplied to the previous architecture drawings.

In FIG. 14, one example control arrangement for use in thelow-frequency-path power supply 518, both in FD mode and in ET modeoperates substantially in the same manner as described in FIG. 5.However, in contrast to FIG. 5, the error amplifier 529 receives anoutput from analog multiplexer 1107, which is fed from either an FDSenseinput or the output from the subtractor 1320. As such, the outputvoltage 1310 can be used directly as the control voltage to a pulsewidthmodulator 532 in the low-frequency-path power supply 518 in order toproduce the appropriate current to apply to the coupling network. Thesubtractor 1320 subtracts the output of the linear amplifier 504, whichis powered by the PWM 1336 of the HF supply module 1306 in the samemanner as FIG. 13, from the supply voltage 528 applied to the PA 424.

The function and characteristics of inductance 621, capacitor 1332,inductance 622, capacitance 1333, inductance 1337, and capacitance 1335are similar to that described with reference to FIG. 13, in that theyact as a 4^(th) order low pass filter applied to the supply voltage 528of PA 424 to reduce any current ripple.

FIG. 15 illustrates a simplified example flowchart 1500 to supportenvelope tracking (ET) in a transmitter chain. The flowchart starts instep 1505 with, say, the transmitter commencing a power level updateprocess. The transmitter starts to modulate signals for transmissionusing, say, a pre-determined modulation scheme in step 1510 and sets aninitial radio frequency output power level of the transmitter in step1515. A determination is then made as to whether envelope tracking isrequired, as shown in step 1520. If envelope tracking is beneficial orrequired in step 1520, then a determination is made as to whether thecurrent mode being used is envelope tracking, as in step 1525. If thecurrent mode of operation is envelope tracking in step 1525, one or moremodulator parameters are adjusted within the transmitter chain, in step1530, an ET to ET transition is performed in step 1535 and the processends in step 1540.

However, if the current mode of operation is not envelope tracking, instep 1525, one or more modulator parameters are adjusted within thetransmitter chain, in step 1550, a FD to ET transition is performed instep 1565, disabling FD mode and enabling ET mode, and the process endsin step 1540.

Referring back to step 1520, if the mode of operation required is notenvelope tracking, a determination is made as to whether the currentmode of operation is FD, as shown in step 1545. If the current mode ofoperation is FD, in step 1545, one or more modulator parameters areadjusted within the transmitter chain, in step 1550, a FD to FDtransition is performed in step 1555 and the process ends in step 1540.However, if the current mode of operation is not FD, the modulatorparameters are adjusted within the transmitter chain, in step 1570.Thereafter an ET to FD transition in step 1575 is performed, causing theenvelope tracking mode of operation to be disabled and the fixed drainmode enabled, in step 1575 and the process ends in step 1540.

In some examples, some or all of the steps illustrated in the flowchartmay be implemented in hardware and/or some or all of the stepsillustrated in the flowchart may be implemented in software. In someexamples, the aforementioned steps of FIG. 15 may be re-ordered, whilstproviding the same or similar benefits.

Thus, the hereinbefore examples provide improved power supply integratedcircuits, wireless communication units and methods for power amplifiersupply voltage control that use such linear and efficient transmitterarchitectures, and in particular a wideband power supply architecturethat can provide a supply voltage in power efficient manner.Advantageously, example embodiments of the invention based on an ACcoupled architecture may provide improved efficiency over DC coupledsolutions. For example, in a dc-coupled system where the output of thelinear amplifier is directly connected to the PA supply (i.e. the outputof the modulator), the output cannot exceed the supply of the linearamplifier without forward biasing diodes associated with the outputdevices. However, in an AC coupled system as described, the capacitor isan additional component, with an associated cost. However, the provisionof two modes of operation, in the various architectures described,supports a dual-role of the coupling capacitor. The architectures allowfor the coupling capacitor to function both as the filtering capacitorfor the SMPS in fixed drain mode and as an AC coupling capacitor inenvelope tracking mode.

Advantageously, some of the example embodiments of the invention mayalso provide an ability to drive loads above the power source voltage(Vbat). For example, the linear amplifier may be implemented withgreater than unity gain, which allows output voltages greater thanbattery voltage to be mapped to inputs less than the battery voltage.The dc (average) output voltage, which is set by the compliance of theLF supply SMPS, is limited to voltages less than the battery voltage ifa buck type regulator is used. However the output of the modulator isthe combination (addition) of the DC and AC components. Positive ACvoltages, applied at the output of the amplifier, will drive the outputhigher above the average level, i.e. above the battery voltage. Thisonly works in a transient manner, the DC voltages still remains belowbattery voltage, and relies on the capacitor's ability to maintain a DCvoltage across and act as a level shifter. The presence of an inductorbetween the output of the modulator and switching devices of the LFSupply SMPS is necessary to enable the voltage to momentarily exceed thebattery voltage.

Advantageously, some example embodiments of the invention provide anability to switch between an ET mode of operation and a FD mode ofoperation, dependent upon the prevailing operational conditions. Inparticular, an ability to reconfigure a SMPS power supply from an ETmode of operation to a fixed drain mode of operation, at least for aperiod of time, may negate or reduce a capacitance cost of thearchitecture, as the AC-coupling capacitor may be re-used in an FD modeof operation as a filter capacitor.

Referring now to FIG. 16, there is illustrated a typical computingsystem 1600 that may be employed to implement signal processingfunctionality in embodiments of the invention. Computing systems of thistype may be used in access points and wireless communication units.Those skilled in the relevant art will also recognize how to implementthe invention using other computer systems or architectures. Computingsystem 1600 may represent, for example, any general purpose computingdevice as may be desirable or appropriate for a given application orenvironment. Computing system 1600 can include one or more processors,such as a processor 1604. Processor 1604 can be implemented using ageneral or special-purpose processing engine such as, for example, amicroprocessor, microcontroller or other control module. In thisexample, processor 1604 is connected to a bus 1602 or othercommunications medium.

Computing system 1600 can also include a main memory 1608, such asrandom access memory (RAM) or other dynamic memory, for storinginformation and instructions to be executed by processor 1604. Mainmemory 1608 also may be used for storing temporary variables or otherintermediate information during execution of instructions to be executedby processor 1604. Computing system 1600 may likewise include a readonly memory (ROM) or other static storage device coupled to bus 1602 forstoring static information and instructions for processor 1604.

The computing system 1600 may also include information storage system1610, which may include, for example, a media drive 1612 and a removablestorage interface 1620. The media drive 1612 may include a drive orother mechanism to support fixed or removable storage media, such as ahard disk drive, a floppy disk drive, a magnetic tape drive, an opticaldisk drive, a compact disc (CD) or digital video drive (DVD) read orwrite drive (R or RW), or other removable or fixed media drive. Storagemedia 1618 may include, for example, a hard disk, floppy disk, magnetictape, optical disk, CD or DVD, or other fixed or removable medium thatis read by and written to by media drive 1612. As these examplesillustrate, the storage media 1618 may include a computer-readablestorage medium having particular computer software or data storedtherein.

In alternative embodiments, information storage system 1610 may includeother similar components for allowing computer programs or otherinstructions or data to be loaded into computing system 1600. Suchcomponents may include, for example, a removable storage unit 1622 andan interface 1620, such as a program cartridge and cartridge interface,a removable memory (for example, a flash memory or other removablememory module) and memory slot, and other removable storage units 1622and interfaces 1620 that allow software and data to be transferred fromthe removable storage unit 1618 to computing system 1600.

Computing system 1600 can also include a communications interface 1624.Communications interface 1624 can be used to allow software and data tobe transferred between computing system 1600 and external devices.Examples of communications interface 1624 can include a modem, a networkinterface (such as an Ethernet or other NIC card), a communications port(such as for example, a universal serial bus (USB) port), a PCMCIA slotand card, etc. Software and data transferred via communicationsinterface 1624 are in the form of signals which can be electronic,electromagnetic, and optical or other signals capable of being receivedby communications interface 1624. These signals are provided tocommunications interface 1624 via a channel 1628. This channel 1628 maycarry signals and may be implemented using a wireless medium, wire orcable, fiber optics, or other communications medium. Some examples of achannel include a phone line, a cellular phone link, an RF link, anetwork interface, a local or wide area network, and othercommunications channels.

In this document, the terms ‘computer program product’,‘computer-readable medium’ and the like may be used generally to referto media such as, for example, memory 1608, storage device 1618, orstorage unit 1622. These and other forms of computer-readable media maystore one or more instructions for use by processor 1604, to cause theprocessor to perform specified operations. Such instructions, generallyreferred to as ‘computer program code’ (which may be grouped in the formof computer programs or other groupings), when executed, enable thecomputing system 1600 to perform functions of embodiments of the presentinvention. Note that the code may directly cause the processor toperform specified operations, be compiled to do so, and/or be combinedwith other software, hardware, and/or firmware elements (e.g., librariesfor performing standard functions) to do so.

In an embodiment where the elements are implemented using software, thesoftware may be stored in a computer-readable medium and loaded intocomputing system 1600 using, for example, removable storage drive 1622,drive 1612 or communications interface 1624. The control module (in thisexample, software instructions or computer program code), when executedby the processor 1604, causes the processor 1604 to perform thefunctions of the invention as described herein.

In particular, it is envisaged that the aforementioned inventive conceptcan be applied by a semiconductor manufacturer to any integrated circuitcomprising a power supply circuit for a PA. It is further envisagedthat, for example, a semiconductor manufacturer may employ the inventiveconcept in a design of a stand-alone device, such as a power supplymodule, or application-specific integrated circuit (ASIC) and/or anyother sub-system element. Alternatively, the examples of the inventionmay be embodied in discrete circuits or combination of components.

It will be appreciated that, for clarity purposes, the above descriptionhas described embodiments of the invention with reference to differentfunctional units and processors. However, it will be apparent that anysuitable distribution of functionality between different functionalunits or processors, for example with respect to the power supplycircuitry or signal conditioning circuits or amplifier circuits may beused without detracting from the invention. For example, functionalityillustrated to be performed by separate processors or controllers may beperformed by the same processor or controller. Hence, references tospecific functional units are only to be seen as references to suitablemeans for providing the described functionality, rather than indicativeof a strict logical or physical structure or organization.

Aspects of the invention may be implemented in any suitable formincluding hardware, software, firmware or any combination of these. Theinvention may optionally be implemented, at least partly, as computersoftware running on one or more data processors and/or digital signalprocessors or configurable module components such as field programmablegate array (FPGA) devices. Thus, the elements and components of anembodiment of the invention may be physically, functionally andlogically implemented in any suitable way. Indeed, the functionality maybe implemented in a single unit, in a plurality of units or as part ofother functional units.

Although the present invention has been described in connection withsome embodiments, it is not intended to be limited to the specific formset forth herein. Rather, the scope of the present invention is limitedonly by the accompanying claims. Additionally, although a feature mayappear to be described in connection with particular embodiments, oneskilled in the art would recognize that various features of thedescribed embodiments may be combined in accordance with the invention.In the claims, the term ‘comprising’ does not exclude the presence ofother elements or steps.

Furthermore, although individually listed, a plurality of means,elements or method steps may be implemented by, for example, a singleunit or processor. Additionally, although individual features may beincluded in different claims, these may possibly be advantageouslycombined, and the inclusion in different claims does not imply that acombination of features is not feasible and/or advantageous. Also, theinclusion of a feature in one category of claims does not imply alimitation to this category, but rather indicates that the feature isequally applicable to other claim categories, as appropriate.

Furthermore, the order of features in the claims does not imply anyspecific order in which the features must be performed and in particularthe order of individual steps in a method claim does not imply that thesteps must be performed in this order. Rather, the steps may beperformed in any suitable order. In addition, singular references do notexclude a plurality. Thus, references to ‘a’, ‘an’, ‘first’, ‘second’,etc. do not preclude a plurality.

Thus, an improved power supply integrated circuit(s), wirelesscommunication unit (s) and methods for power amplifier supply voltagecontrol that use linear and efficient transmitter architectures, and inparticular a wideband power supply architecture that can provide asupply voltage in power efficient manner therefor, have been described,wherein the aforementioned disadvantages with prior art arrangementshave been substantially alleviated.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. An integrated circuit for providing a powersupply to a radio frequency (RF) power amplifier (PA), the integratedcircuit comprising: a low-frequency power supply path comprising aswitching regulator; and a high-frequency power supply path arranged toregulate an output voltage of a combined power supply at an output portof the integrated circuit for coupling to a load wherein the combinedpower supply is provided by the low-frequency power supply path andhigh-frequency power supply path; wherein the high-frequency powersupply path comprises: an amplifier comprising a voltage feedback andarranged to drive a power supply signal on the high-frequency powersupply path; and a high-frequency-path supply module arranged to providea high frequency supply to drive the amplifier, where thehigh-frequency-path supply module comprises a pulse-width modulatoroperably coupled to the high frequency supply via a filter and arrangedto provide a filtered pulse-width modulated signal to the high frequencysupply path.
 2. The integrated circuit of claim 1 wherein the amplifieris a linear amplifier comprising a first input for receiving the voltagefeedback and a second input arranged to receive a modulated envelopeinput signal.
 3. The integrated circuit of claim 1 wherein the filter isan inductance-capacitance filter with a node coupling a first inductanceand first capacitance arranged to fix a dc operating point of the linearamplifier.
 4. The integrated circuit of claim 1 wherein the filteredpulse-width modulated signal fixes a dc operating point of the linearamplifier.
 5. The integrated circuit of claim 1 wherein the switchingregulator of the low-frequency power supply path controls an averageoutput voltage of the amplifier by use of a capacitor acting as anintegrator.
 6. The integrated circuit of claim 1 wherein the powersupply is a hybrid wideband power supply comprising a switch mode powersupply.
 7. The integrated circuit of claim 1 further comprising a modecontrol module arranged to select between at least an envelope trackingmode of operation and a fixed drain mode of operation of the amplifier.8. The integrated circuit of claim 7 wherein, in the fixed drain mode ofoperation of the amplifier, the integrated circuit further comprises afirst output port coupled to the low-frequency power supply path and asecond output port coupled to the amplifier for coupling to the RF PAvia an inductance-capacitance network.
 9. The integrated circuit ofclaim 8 wherein the first output port and second output port facilitatecoupling a fourth-order low pass filter to the combined power supply ofthe RF PA.
 10. The integrated circuit of claim 9 wherein a secondinductance and second capacitance of the fourth-order low pass filterare arranged to reduce current ripple on a pulse width modulated signalon the low-frequency power supply path.
 11. The integrated circuit ofclaim 1 further comprising a subtractor module operably coupled to andindependent from the low-frequency power supply path and arranged tosubtract an instantaneous load current at the output of the linearamplifier from the combined modulated power supply at the output port ofthe integrated circuit.
 12. The integrated circuit of claim 10 wherein,in the envelope tracking mode of operation, a feedback signal for thelow-frequency power supply path takes as its input the output of thesubtractor module.
 13. The integrated circuit of claim 11 wherein theoutput of the subtractor module is input to a summing junction arrangedto sum the output of the subtractor module with a sensed output of thelinear amplifier.
 14. The integrated circuit of claim 12 wherein thesensed output of the linear amplifier is converted to voltage by acurrent to voltage converter before being input to the summing junction.15. The integrated circuit of claim 10 wherein the instantaneous loadcurrent at the output of the linear amplifier comprises a slowly-varyingterm that reflects an integrated difference between the output voltageof the linear amplifier and a desired value.
 16. The integrated circuitof claim 10 wherein the low-frequency power supply path comprises apulse width modulator arranged to respond to a control signal outputfrom the subtractor module to produce a low frequency output current.17. The integrated circuit of claim 10 wherein the low-frequency powersupply path comprises a comparator having an output that provides thecombined power supply at the output port of the integrated circuit and afirst input connected to an analog multiplexer arranged to multiplex anoutput from the subtractor module with a sensed output current from thecomparator output.
 18. A wireless communication unit comprising a radiofrequency (RF) power amplifier (PA) and a power supply for providing apower supply to the RF PA, the wireless communication unit comprising: alow-frequency power supply path comprising a switching regulator; and ahigh-frequency power supply path arranged to regulate an output voltageof a combined power supply for coupling to a load wherein the combinedpower supply is provided by the low-frequency power supply path andhigh-frequency power supply path; wherein the high-frequency powersupply path comprises: an amplifier comprising a voltage feedback andarranged to drive a power supply signal on the high-frequency powersupply path; and a high-frequency-path supply module arranged to providea high frequency supply to drive the amplifier, where thehigh-frequency-path supply module comprises a pulse-width modulatoroperably coupled to the high frequency supply via a filter and arrangedto provide a filtered pulse-width modulated signal to the high frequencysupply.
 19. A wireless communication unit comprising a radio frequency(RF) power amplifier (PA) and a power supply for providing a powersupply to the RF PA, the wireless communication unit comprising: alow-frequency power supply path comprising a switching regulator; and ahigh-frequency power supply path comprising an amplifier coupled to aload through a capacitor; wherein the output of the low-frequency powersupply path is controlled according to an output of the amplifiercoupled to one end of the capacitor and a combined modulated powersupply provided by the low-frequency power supply path andhigh-frequency power supply path coupled to another end of thecapacitor.
 20. The wireless communication unit of claim 19 furthercomprising a subtractor module operably coupled to the low-frequencypower supply path and arranged to subtract an instantaneous load currentat the output of the amplifier from the combined modulated power supplyprovided by the low-frequency power supply path and high-frequency powersupply path.
 21. The wireless communication unit of claim 20 wherein, inthe envelope tracking mode of operation, a feedback signal for thelow-frequency power supply path takes as its input the output of thesubtractor module.
 22. The wireless communication unit of claim 20wherein the output of the subtractor module is input to a summingjunction arranged to sum the output of the subtractor module with asensed output of the amplifier.
 23. The wireless communication unit ofclaim 22 wherein the sensed output of the linear amplifier is convertedto voltage by a current to voltage converter before being input to thesumming junction.
 24. The wireless communication unit of claim 20wherein the instantaneous load current at the output of the amplifiercomprises a slowly-varying term that reflects an integrated differencebetween the output voltage of the amplifier and a desired value.
 25. Thewireless communication unit of claim 20 wherein the low-frequency powersupply path comprises a pulse width modulator arranged to respond to acontrol signal output from the subtractor module to produce a lowfrequency output current.
 26. The wireless communication unit of claim19 wherein a voltage of the capacitor is tended to be equal to a desiredreference value.
 27. The wireless communication unit of claim 19 whereinan instantaneous output current of the amplifier is tended to be zero bysupplying more current through the low-frequency path when the outputcurrent of the amplifier is high.